The present invention relates to a method and an apparatus for matching fingerprints.
The principle of the prior art concerning the matching of fingerprints is as follows. A fingerprint is composed of lines known as ridges, which have branching parts (bifurcations) and abrupt endings (end points). These bifurcations and end points are known as minutiae. Two fingerprints will be identified with one another if the positions of and relations among pairs of such points match each other as a rule without excess or deficiency.
For details of a fingerprint matching apparatus based on this principle, .reference may be made to the U.S. Pat. No. 4,646,352. When a fingerprint is registered with such apparatus it extracts, and files, the minutiae and inter-minutia relations from the fingerprint to be registered. In collating a newly inputted fingerprint image, its minutiae and interminutia relations are extracted, and the extracted minutiae and their relations are compared with those of filed fingerprints to determine whether the new fingerprint can be identified with one of the filed fingerprints.
This apparatus, however, requires a vast quantity of calculations to extract minutiae and their relations from each fingerprint image.
Therefore, this apparatus proves highly useful in criminal investigations using a large general-purpose computer or a supercomputer in which a suspect is to be identified by the fingerprints left by the offender.
However, where the fingerprint of the individual to be identified is already known, such as in entrance control, and a fingerprint presented for entrance clearance by that particular individual is to be collatted with his or her registered fingerprint, quick processing low-cost processing apparatus with modest computing capacity is required.
For a technology meeting this requirement, reference may be made to Koichiro Morita and Ko Asai, "Automatic fingerprint identification terminal for personal verification" in PROCEEDINGS OF SPIE - The International Society for Optical Engineering, Society of Photo-Optical Instrumentation Engineers, 1986, pp. 174-181. The terminal described in this literature, at the time of registration when no particularly quick processing is demanded, executes the processing to extract minutiae and their relations to prepare and file a list of the minutiae of the fingerprint to be registered. On the other hand, at the time of collation when high-speed processing is needed, information on the minutiae in the filed list is referenced, the presence or absence of the minutiae referred to in the inputted fingerprint image is checked and, if they are present, the number of ridges is counted as representing the relations among the minutiae. Then the inputted fingerprint is collated according to the presence or absence of the minutiae and the number of ridges to identify it, or deny its identity, with the registered fingerprint.
Thus collation by a processing apparatus with limited computing capacity uses a method to check whether the minutiae stated in the list of registered minutiae are present and, if they are, whether the number of ridges in every pair of such minutiae is equal to what is registered.
Therefore, this method has a first disadvantage of recognizing an identity and processing accordingly as long as the minutiae registered in the list of minutiae are present and the number of ridges between every pair of minutiae is equal to what is registered .even though the inputted fingerprint has minutiae which should not be in the registered one. In other words, it is highly possible that wrong recognition may occur because of the absence of collation information in the area where no minutiae are present.
There is another disadvantage, which concerns security. It is supposed here that a mechanism requiring the execution of collation and the result thereof is not capable of detecting aforementioned minutiae and of counting the number of ridges between them. Such an apparatus exists having such capabilities exists external to the mechanism, but the possible leak of the contents of the minutia list out of the mechanism should be prevented.
A first specific example of this situation may be a case in which a person desiring access to an IC card is to be identified by his or her fingerprint.
Usually, an integrated circuit built into an IC card has no video processing capability due to a variety of constraints. Moreover, an available external apparatus is likely to be too small a terminal unit to be able to quickly prepare a list of minutiae from an inputted fingerprint image.
There is the disadvantage that, in this situation, providing the list of minutiae registered in the IC card to the external apparatus would make it impossible for the identification function to be performed.
A second specific example concerns a system in which a center for concentrated management of the lists of registered minutiae and terminal units installed where entrance control is performed are linked by communication lines.
None of the terminal units in this system would be capable of quickly preparing a list of minutiae from an inputted fingerprint image. Further there might be the disadvantage that it is not always possible to send the inputted fingerprint image to the center because of line capacity. SUMMARY OF THE INVENTION
A main object of the present invention is to provide a method and an apparatus for the matching of fingerprints free from the foregoing disadvantages and offering an improved in collation rate.
Another object of the invention is to provide a method and an apparatus for the matching of fingerprints free from the foregoing disadvantages and offering improved security.
A method for the matching of fingerprints according to a first aspect of the present invention comprises:
an inputting step to enter a fingerprint image, and
a collating step to check the collation minutiae of the input fingerprint image, consisting of both characteristic and non-characteristic minutiae, with the collation minutiae already registered in a list of collation minutia records.
An apparatus for the matching of fingerprints according to a second aspect of the invention comprises:
an IC card having minutia record holding means for holding collation minutiae consisting of both characteristic and non-characteristic minutiae, and sending means for sending collation minutia information from the minutia record holding means to an image processing unit, and
the image processing unit having collation minutia searching means responsive to the collation minutia information from the sending means of the IC card for searching the collation minutiae and sending the result of search to said IC card.
An apparatus for the matching of fingerprints according to a third aspect of the invention is an apparatus according to said second aspect of the invention wherein the minutia record holding means in the IC card is accessed using random numbers.
An apparatus for the matching of fingerprints according to a fourth aspect of the invention is an apparatus according to said second aspect of the invention wherein the IC card sets the permissible frequency of sending by said sending means in response to the result of a search from the collation minutia searching means of said image processing unit at any desired value greater than a predetermined level.